1. Field of the Invention
The present invention relates to a process for producing an electrophotographic photosensitive member, and an electrophotographic photosensitive member produced by the same process, more particularly to a process for producing an electrophotographic photosensitive member which uses a coating solution containing a specific solvent for a charge-transporting layer, and an electrophotographic photosensitive member produced by the same process.
2. Related Background Art
Recently, organic electrophotographic photosensitive members with photosensitive layers containing a variety of organic photoconductive compounds as major components have been extensively studied and developed. Especially, function-separated electrophotographic photosensitive members, in which charge-generating and charge-transporting functions are separately provided by different substances, have been extensively studied, because of various advantages. For example, they have wider selections of their materials for each function, and they can be produced relatively easily to have the desired functions. Many have been already commercialized.
The function-separated electrophotographic photosensitive member is generally produced by applying a coating solution in which a solid organic compound is dissolved in an organic solvent onto a substrate using an adequate method selected from a variety of coating methods and drying.
However, there are not many organic solvents which have a high dissolving power and an adequate boiling point, especially suitable for commercial production, contrary to expectations.
It is needless to say that the solvent for production of an electrophotographic photosensitive member must have a sufficient dissolving power and an adequate boiling point to give the desired product, and, at the same time, must not adversely affect the characteristics of the electrophotographic photosensitive member for which it is used. Recently, those solvents which can satisfy all of these requirements are increasingly in demand.
In the case of a laminated type electrophotographic photosensitive member in particular, with a laminated structure to have the charge-generating and charge-transporting functions separately, the charge-transporting layer (around 10 to 40 xcexcm thick) accounts for most of the thickness of the photosensitive layer. Therefore, the solvent for the coating solution for the charge-transporting layer must satisfy various requirements, such as high dissolving power and adequate boiling point, to prevent the solution from remaining in the photosensitive layer, because the solvent may trickle down from the layer when its boiling point is excessively high, and it may damage the electrophotographic characteristics of the layer when it remains as an impurity in the layer.
Polycarbonate and polyarylate resins have been used as excellent binder resins for the charge-transporting layer.
However, the solvents for dissolving these resins to prepare the coating solutions for the charge-transporting layer are frequently halogen-containing organic solvents, e.g., methylene chloride, ethylene chloride, chloroform, monochlorobenzene, dichlorobenzene and a combination thereof. There are a number of halogen-free organic solvents, e.g., acetone, acetic acid, methylethylketone, toluene, tetrahydrofuran (THF), dioxane and cyclohexanone. However, there are few halogen-free organic solvents which satisfy all of the requirements for dissolving polycarbonate or polyarylate resin, e.g., sufficient dissolving power, adequate boiling point to prevent, e.g., trickling down while the coating layer is formed, and characteristics which make the electrophotographic photosensitive member sufficiently sensitive. The solvent is particularly required to have a sufficient dissolving power for a high-molecular-weight polycarbonate or polyarylate resin as the binder resin, when it is used for the charge-transporting layer, which has generally a thickness of 15 xcexcm or more.
The good solvents include tetrahydrofuran as a cyclic ether having an oxygen atom in the molecule, and dioxane having two oxygen atoms in the molecule. However, tetrahydrofuran or the like is structurally unstable, needing a fairly large quantity of the stabilizer or the like which can serve as the carrier trap. Dioxane or the like, on the other hand, is highly toxic and suspected to be carcinogenic, and its use in the production line must be avoided as far as possible.
Further, the electrophotographic characteristics frequently vary greatly depending on the solvent used for the coating solution. Moreover, type of the solvent to be used is very important for productivity, and compatibility with the charge-transporting substance and binder resin. Therefore, organic solvents having better characteristics in consideration of the above are in demand.
It is an object of the present invention to provide a process which can suitably produce, under widely varying coating conditions, an electrophotographic photosensitive member showing excellent potential characteristics, durability, image characteristics and resolution for an extended period from an initial stage of image formation, and an electrophotographic photosensitive member produced by the same method.
The present invention provides a process for producing an electrophotographic photosensitive member which has a charge-generating layer and a charge-transporting layer on a substrate, comprising steps of applying a solution containing a charge-transporting material, binder resin, dimethoxymethane and an aromatic hydrocarbon-based solvent having a boiling point of 130xc2x0 C. or higher, and drying the solution, to form the charge-transporting layer.
The present invention also provides an electrophotographic photosensitive member comprising a substrate, a charge-generating layer and a charge-transporting layer, wherein the charge-transporting layer is formed by applying a solution containing a charge-transporting material, binder resin, dimethoxymethane and an aromatic hydrocarbon-based solvent having a boiling point of 130xc2x0 C. or higher, and drying the solution.